Synchronized/variable force feedback power steering

Abstract

A steering tiller and a steered wheel(s) of a steer-by-wire steering system of a materials handling vehicle are synchronized with one another and a virtual coupling force is exerted on the steering tiller to maintain synchronization. A motor or brake is associated with the steering tiller and the positions of the tiller and the steered wheel(s) are monitored and used to control the motor or brake to apply the virtual coupling force to the tiller. Thus, an operator of the vehicle receives feedback corresponding approximately to that experienced in a mechanically coupled steering system so that synchronism is maintained between the tiller and the steered wheel(s). In this way, if the operator attempts to oversteer or outrun the steered wheel(s) by rapid rotation of the tiller, a force proportional to the operator's action is applied to oppose that action. Synchronization can be set up with the tiller set to a desired position selected by the operator, for example to selected a desired tiller spinner straight ahead position.

What is claimed is:  
     
       1. A method for operating a steer-by-wire power steering system for a materials handling vehicle comprising the steps of: 
       monitoring angular position of a steering tiller for said materials handling vehicle;  
       monitoring angular position of a steered wheel for said materials handling vehicle;  
       determining a difference between the position of said steering tiller and the position of said steered wheel; and  
       generating a counter rotation force that opposes turning of said steering tiller by an operator of said materials handling vehicle in response to said difference by braking said steering tiller.  
     
     
       2. A method for operating a steer-by-wire power steering system for a materials handling vehicle as claimed in  claim 1  further comprising the step of synchronizing the positions of said steering tiller and said steered wheel to one another. 
     
     
       3. A method for operating a steer-by-wire power steering system for a materials handling vehicle as claimed in  claim 2  wherein said step of synchronizing the positions of said steering tiller and said steered wheel to one another comprises the steps of: 
       slipping said steering system for movements of said system in a direction which reduces offset error between said steering tiller and said steered wheel; and  
       preventing slip of said steering system for movements of said system in a direction which increases offset error between said steering tiller and said steered wheel.  
     
     
       4. A method for operating a steer-by-wire power steering system for a materials handling vehicle comprising the steps of: 
       monitoring angular position of a steering tiller for said materials handling vehicle;  
       monitoring angular position of a steered wheel for said materials handling vehicle;  
       moving said steering tiller to a position preferred by an operator of said materials handling vehicle to correspond to a defined steered wheel position;  
       moving said steered wheel to said defined steered wheel position; and  
       setting said preferred tiller position and said defined steered wheel position to correspond to one another so that movements of said steered wheel are made from said defined steered wheel position in correspondence with movement of said steering tiller from said operator preferred position.  
     
     
       5. A method for operating a steer-by-wire power steering system for a materials handling vehicle as claimed in  claim 4  wherein said step of moving said steering tiller is performed at key on prior to startup of said materials handling vehicle and said step of moving said steered wheel is performed upon startup of said materials handling vehicle. 
     
     
       6. A method for operating a steer-by-wire power steering system for a materials handling vehicle as claimed in  claim 5  wherein said step of moving said steering tiller is performed manually by said operator. 
     
     
       7. A method for operating a steer-by-wire power steering system for a materials handling vehicle as claimed in  claim 4  wherein said defined steered wheel position corresponds to straight ahead movement for said materials handling vehicle. 
     
     
       8. A method for operating a steer-by-wire power steering system for a materials handling vehicle comprising the steps of: 
       monitoring angular position of a steering tiller for said materials handling vehicle;  
       monitoring angular position of a steered wheel for said materials handling vehicle;  
       moving said steered wheel toward the position of said steering tiller; and  
       synchronizing said steered wheel and said steering tiller upon the position of said steered wheel substantially matching the position of said steering tiller.  
     
     
       9. A method for operating a steer-by-wire power steering system for a materials handling vehicle as claimed in  claim 8  further comprising the step of operating a motor to move said steering tiller toward the position of said steered wheel.